It is commonplace to use a resilient sealing strip such as rubber, inserted into the gap between a roadway sections of a carriage-way, bridge etc. to close and seal the gap. Structural and retaining members are included at the edges of the gap to maintain the sealing strip in position, and allow for its necessary tension to effect its sealing function. It is, however, often desirable to use two or three of such sealing strips arranged side by side to seal the gap between the roadway sections, with an intermediate retaining structural member between the seals, since a relatively large gap may be necessary to allow for expansion, particularly on bridges, and sealing strips of large width are difficult to handle and install, and do not perform satisfactorily in use.
Many highway authorities demand that expansion joints, particularly for use between roadway sections of bridges, effect a watertight seal of the joint at all times. The authorities seek to ensure that there is no risk of contamination of rivers, terrain etc. below the bridge by liquids or the like dropping from the bridge roadway. A particular hazard in this respect is road salt, which may be applied to remove ice from the bridge roadway sections.